1. Field of the Invention
The present invention relates to film formation systems and film formation methods, and, more particularly, to a system for manufacturing a photoelectric element.
2. Description of Related Art
Currently, the photoelectric conversion efficiency of a representative semiconductor photoelectric element, such as a light emitting diode (LED) or a solar cell, is one of the most significant efficiency indexes, as far as device efficacy is concerned. Related to the conversion efficiency, an even and smooth surface may have a higher light reflection rate, as compared to an uneven surface. As such, an uneven surface is advantageous. To effectively raise the conversion efficiency, a manufacturer may fabricate an uneven microstructure that includes concave and convex portions on a surface of the element. As a result, the roughness of the surface of the element has a significant influence on the conversion efficiency. In general, the microstructure is composed of ordered and disordered microstructures. A disordered microstructure is achieved by a chemical etching process, while an ordered microstructure is achieved by a resist lithography process.
In the prior resist lithography process, a dried film is formed on a surface of a wafer and acts as a photomask, then photomask holes are formed with the use of exposure and development processes to expose a part of surface of the wafer, a micro-etching process is then performed in the photomask holes to roughen the exposed surface of the wafer, and finally the dried film is removed. However, the prior resist lithography process has a long manufacturing time, and the dried film has a high cost and is likely to contaminate the environment. Accordingly, a photomask composed of nano-spheres has been developed to replace the dried film. Such a photomask has low cost, is environment-friendly, and has a short manufacturing time.
According to the prior art, the photomask composed of the nano-spheres is manufactured in an immersion-startup way. Initially, a container is filled with a liquid having a plurality of nano-spheres. Then, a wafer is immersed into the liquid, allowing the nano-spheres to gather on a surface of the wafer. Finally, start up movement of the wafer, allowing the nano-spheres to be adhered to the surface of the wafer and form a photomask composed of the nano-spheres. However, the speed for the wafer to be started up at is closely related to the tightness of the photomask. Too high a startup speed causes the nano-spheres to be unable to be adhered to the surface of the wafer, and the photomask may have a large breach, which results in the formation of a large concave portion, rather than a microstructure, during a subsequent etching process. Too low a startup speed causes the nano-spheres to be stacked on the surface of the wafer in a multi-layered form, which results in difficulty forming a breach on the photomask and forming a microstructure during a subsequent etching process. In this regard, a wafer manufacturing process is developed without considering the startup speed.
FIGS. 1A-1E illustrate a film formation method adopting nano-sphere lithography according to the prior art. As shown in FIG. 1A, a container 10 having a diameter of 15 cm is provided. Water 100 is injected into the container 10. Then, as shown in FIGS. 1B and 1C, an injector or a pipette contacts the water surface, and injects along the water surface ethanol solution 300a (having a concentration of 10% or 8%) having a plurality of nano-spheres 301, allowing the nano-spheres 301 to be scattered loosely on the water surface. The ethanol solution 300a pulls the nano-spheres 301 to move toward an edge of the container 10, allowing the nano-spheres 301 to gather and form a film layer 30′ having an opening, for use as a required photomask film. As shown in FIG. 1D, a substrate 3 (which is a 1 cm2 wafer) is placed through the opening 302 into the water 100 contained in the container 10, with the surface of the substrate 3 exactly opposing to and contacting the bottom of the film layer 30′, allowing the film layer 30′ to be engaged with the surface of the substrate 3. Then, as shown in FIG. 1E, the substrate 3 is removed by lifting upwards from the water surface, allowing the surface of the substrate 3 to have the film layer 30′ that acts as a photomask. Subsequently, an etching process to roughen the surface may be performed.
However, though the aforesaid nano-sphere lithography process need not take the startup speed into consideration, the process cannot manufacture a photomask on a wafer having a large area, but only on a wafer having a small area, such as 1 cm2. Therefore, the demand for larger-sized areas is not satisfied.
Additionally, the film layer 30′ on the water surface in the container 10 has to have a space (e.g., the opening 302) reserved for release pressure. Because the nano-spheres 301 may not occupy the whole water surface, or the nano-spheres 301 may contact the inner wall 10a of the container 10 and burst, the nano-spheres 301 may occupy as much as 70% of the water surface. Therefore, a photomask required for a wafer having a large area may not be produced. If the nano-spheres 301 occupy the whole water surface, as in the step shown in FIG. 1D, the substrate 3 cannot be placed into the water 100 without disturbing the film layer 30′. If attempted, the film layer 30′ can exhibit damage, like a cracked lattice, which affects the adhering force of the nano-spheres 301.
Therefore, finding a way to prevent the aforesaid problems of the prior art has become one of the most urgent issues in the art.